In order to determine the transmission characteristics of a waveguide directional coupler, it is necessary to first determine the size and location of couplings within the waveguide. Often the size and location of such couplings are unknown. However, the couplings are in the interior of the waveguide and are obscured from view and, hence, the size and location of the couplings cannot be visually determined.
Conventionally, the size and location of waveguide couplings are determined by X-ray techniques. However, such X-ray measurements are expensive to obtain and time consuming to perform, and often do not reliably determine the absolute size and location of the waveguide couplings.